1. Field of Invention
The present invention relates in general to electric motors, and more particularly to electric motors of a two rotor single stator type which comprises outer and inner rotors which rotate around and within a common stator. More specifically, the present invention is concerned with a stator for the two rotor single stator type electric motor.
2. Description of Related Art
One electric motor of the above-mentioned type is shown in Japanese Laid-open Patent Application (Tokkai) 2000-14086. In the electric motor of this published application, upon feeding a compound electric current to a common stator, two rotors, that is, outer and inner rotors are rotated around and within the common stator respectively. By varying the nature of the compound electric current fed to the stator, rotation of the outer rotor and that of the inner rotor are individually controlled.
The stator of the electric motor of the published application comprises a stator core that includes a plurality of stator teeth that are circumferentially arranged around a common axis of the motor at evenly spaced intervals. Each stator tooth has a generally rectangular parallelepiped shape and includes a plurality of pressed flat magnetic steel plates that are aligned along the common axis while intimately and closely contacting to one another. Thus, upon assembly, the stator core has a waterwheel shape having a plurality of vanes (viz., stator teeth) circumferentially arranged about an axis of the stator. Each stator tooth has a coil that is put therearound making round-trips in a direction parallel with the common axis. The stator core thus assembled is sandwiched between two axially spaced supporting brackets and tightened by a plurality of bolts and nuts. Each bolt extends in a direction parallel with the common axis in and along a space defined between adjacent two of the stator teeth. The space is filled with a molded plastic. Thus, upon completion of assembly, the stator has a cylindrical shape.
In order to effectively generate a magnetic flux in the magnetic path, each stator tooth has at radially outer and inner ends thereof yoke portions that project in a circumferential direction. Due to provision of such yoke portions, an outward magnetic resistance (which will be referred to “magnetic bypass resistance” hereinafter) of each stator tooth is increased, and thus, undesired outward dispersal of the magnetic flux through the stator tooth is suppressed or at least minimized.
As is described hereinabove, the space defined between adjacent two of the stator teeth is filled with a molded plastic through which the connecting bolts extend axially. One end of each bolt is connected to a motor housing, so that the stator is held by the motor housing in a so-called cantilever holding way. Also the bolts function to generate the magnetic bypass resistance.